Astronomers have shown that dead stars known as white dwarfs can re-ignite and explode as supernovas.

The discovery appears to solve a mystery surrounding the nature of a particular category of stellar explosions known as Type Ia supernovas.

Theorists suspected that white dwarfs could explode due to a disruptive interaction with a companion star, but lacked definitive evidence until now.

Details of the research appear in the journal Nature.

The "smoking gun" in this case was the detection of radioactive nuclei being generated by nuclear fusion in the cosmic blast.

Astronomers have long had the tools to detect the signature of this fusion, but had to wait for a supernova to explode nearby in order to begin their observations.

Towards the end of its life, a star with the mass of the Sun will shed its outer layers as its core shrinks down to become a white dwarf. Left to their own devices, single white dwarfs will just cool off slowly over time.

But there is a maximum mass at which a white dwarf can remain stable - a property known as the Chandrasekhar limit, after the Indian-American astrophysicist Subrahmanyan Chandrasekhar.